Fish farming or open ocean aquaculture is the rearing of marine organisms under controlled conditions in exposed high energy ocean environments. The purpose of the open ocean aquaculture is to raise a species of fish in a controlled environment wherein the open ocean allows for the natural cleansing of the holding pen. The open ocean aquaculture facilities consist of cages, holding pens, or the like that can be free floating, secured to a structure, or lowered to the ocean bottom. Open ocean aquaculture also makes use of the vast area of the ocean wherein cage size is not limited, as compared to the placement of cages within bays or the like tightly boarded area. The fish farming industry has enjoyed a steady strong growth for many years and can produce sustainable high quality fish products.
Fish farming has been done for thousands of years, yet in many ways it is still in its infancy. Environmental concerns and labor rates of the developed countries are the new barriers for continued growth of the industry. Offshore aquaculture is among the fasted growing industries today. Fish consumption is rising and wild stocks are unable to meet demand. Many ocean species contain valuable omega 3 oils that are recommended by doctors for good health. These oils are not abundantly found in fresh water species. The health benefits of ocean fish will continue to drive demand for ocean grown fish for decades to come. Offshore aquaculture has not developed in the United States despite the fact that we have the largest Exclusive Economic Zone in the world at 3.4 million square miles.
Historically ocean water fish farming has been done in protected near shore areas where access to the cages has been very good and cleaning and maintaining cage screens has been affordable and not prohibitive due to open sea conditions, distance and increasing labor rates. The netting is usually coated with antifouling material. The nets are removed and cleaned every few weeks and re-dipped in antifouling material, and then reentered into the water. This process is presently under attack in Europe and Canada, because of the environmental impacts of the poisons introduced into the water during the cleaning process and while in use. Thousands of fish cages are doing this worldwide. The antifouling that reaches the ocean or bay floor reduces the ability of the floor to deal with by-products from the fish in the very worst cases. Antifouling paints are also under attack by environmentalist and the most effective antifouling paints are already banned in the U.S.
Today many countries have used and over used the acceptable protected aquaculture sites and are now forced to go offshore to expand. The U.S. is committed to develop an offshore aquaculture plan for federal waters. Most of the U.S acceptable sites are 10 to 70 miles offshore and in areas that are susceptible to severe weather. The solution for severe weather areas is underwater cages that are not affected by surface waves.
The netting from offshore underwater cages cannot be efficiently removed for cleaning. The current solution is to scrub the cage screen underwater to remove fouling. The use of divers is expensive and the small fibers of the net contain small amounts of growth after cleaning and re growth starts immediately.
Holding pens placed in off shore waters employ cages that are lowered and secured to the ocean bottom. Holding pens that are positioned near shore or in bays may consist of floating facilities. Extensive offshore floating facilities are currently found in most costal countries such as Australia, Chile, China, France, Ireland, Italy, Japan and Norway. The United States has only a few open ocean facilities while other countries are experimenting with such facilities such as Panama, Korea, Spain, Mexico, Brazil and other Central and South America countries. Labor offshore has many difficulties including poor working conditions, health risk and transportation costs. This is especially true for underwater cages where divers are required for almost all of the work.
Environmental risk is the most common reason cited for lack of fish farming in the United States. Another reason is suggested likelihood of disease in densely populated farm cages, the risk of disease increased by unwanted growth on the cage. Unwanted growth also reduces oxygenated water flow through the cage and slows fish growth.
Another problem is fish escape. Sharks, sea lions seals and other predators are a constant threat to the stock and integrity of the screen. There is also a risk that escaped fish will breed and interbreed with wild fish and cause problems including upsetting the balance between wild species. Cod fish have been known to chew their way out of cages made from bullet proof vest fibers like Dynema and Trigger fish have chewed their way in to get shrimp. Sharks are drawn to mortalities that sink to the bottom of the cage and have entered cages to enjoy easy feeding and threaten maintenance divers.
The aquaculture facilities may be used to house many different types of fish such as halibut, haddock, cod, flounder, black sea bass, snapper, cobia, yellow tale snapper, cobia, tuna, stripped bass, mahi mahi, and so forth.
Other problems for cages are currents that can change the shape and lower effective volume of the cages, as well as the high maintenance of floating hardware and current cleaning expenses due to the present day net design.
A common problem with such facilities is the exposure to the elements wherein damage to the containment facility can quickly result in a loss of contained fish. For instance, should a facility consist of a cage with netting, a tear in the netting can result in the release of the fish into the open water or the introduction of predators into the cage. Exposure to the elements is not limited to wave action but includes predators such as sharks that work tirelessly to find or create a breech in the netting for access to the fish.
Another approach is the use of steel cages. The increase in strength is beneficial to inhibit a breech but the use of steel in saltwater causes other problems. Steel is susceptible to degradation despite the use of steel protective coatings such as galvanized steel. Further, the use of steel presents associated metal problems such as weight and degradation, and does not address the problems of marine growth. While various growth inhibitor paints are available, inclusion of such paint in close proximately to fish that are to be consumed is not an option.
There are already automatic feeders and harvesting systems to reduce labor requirements, but one of the worse remaining problems is cleaning the cage. Marine growth will attach to most materials and most of the surface is netting that is made from fine fibers that are easy for growth to attach to and is difficult to clean. Cages with excessive marine grown increase drag in the current and risk pulling of the anchoring.
Plastisol® coated steel screens have a smooth non corrosive surface have been used, but Plastisol® leaches out and cracks after a few years. Plastisol® allows growth to attach to it wherein cleaning is still required. Material fatigue remains a problem due to cycle loading of the steel.
The U.S. copper association is experimenting with a copper nickel alloy screen proven effective against growth. The copper alloy is very expensive, heavy and is susceptible to wave action metal fatigue failure. The copper is also poisonous to crustaceans like shrimp. Fatigue failure has already proven to be a problem with galvanized steel screen. Copper alloy screen is slowly removed by electrolysis and has a life expectantly of only 2-4 years in ocean water.
Dynema® and other advanced nettings are available, but it fouls the same as other netting and has found little use due to high cost. All net materials are made of small fibers that make it impossible to clean completely while installed. The small hidden growth that remains after cleaning leaves behind enough material for the start of immediate new growth.
Another product constructed from a PET net is formed like a chain link fence with a double twist at the intersection. It has been shown to be better than netting in some applications, but it is very expensive. Plastic polyethylene screen or netting is available, but it is just not strong enough for ocean demands.
Various concepts have been used to improve netting for cages such as U.S. Pat. No. 6,917,294 which employs conductive wires being integrated into the filaments of the netting. In this disclosure, the wires that are placed through the nets are arranged in a pattern so that if one of the wires is broken in a proximity that is large enough to allow fish to escape an electrical signal is sent to alert the operator of the farm of the break in the net. While this disclosure addresses the need for determining a breech in the netting, the problems of marine growth are not addressed.
Thus, what is lacking in the art is a structure and material for use in aquaculture that has significant strength, capable of most any environmental condition including predator attacks, resisting of grown from barnacles, biomass, grass or the like substances, and is light in weight.